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Ultrafast photoinduced conductivity reduction by bonding orbital control in an incommensurate crystal
No full textInternational audienceIn this paper, we demonstrate the ultrafast reduction of conductivity in an incommensurate crystal structure within hundreds of femtoseconds. This phenomenon stands in stark contrast to most prior experimental investigations where incident light pulses led to increased conductivity. We achieve this by selectively targeting a specific atomic bond using near-infrared light pulses. Our investigation focuses on misfit layered chalcogenide (LaS)1.196VS2, known as LaVS3, a semimetal with incommensurability along one crystallographic direction. Our time-resolved electron dynamics investigation reveals that the conductivity decreases as photoexcited electrons are promoted into localized energy states within vanadium clusters due to the incommensurate structure. These findings offer insights into the potential for controlling electronic properties at femtosecond time scales, with implications for the development of ultrafast electronic devices
Le retard de Sanofi dans la course au vaccin contre la Covid-19. Raisons technologiques, managériales et institutionnelles
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Newly designed metal foam-salt hydrate composite for thermochemical heat storage
No full textInternational audienceThermochemical heat storage system based on the sorption mechanism between water vapor and hygroscopic salts is a promising technology. However, hygroscopic salts have drawbacks such as swelling and agglomeration during hydration/dehydration cycles, which leads to decreasing specific reaction surface and heat and mass transfer problems, resulting in poor cyclic performance and stability. In this context, we propose a composite of open-cell metal foam and calcium chloride for sorption thermal energy storage. An open-cell metal foam host matrix improves the heat and mass transfer kinetics thanks to the porous structure and the high thermal conductivity. Additionally, it offers elevated mechanical strength ensuring the mechanical resistance of the composite. The composite showed significant improvement in cyclic performance compared to that of bulk salt powder. Composites exhibited a stable heat release during cycles, which improved to 5-6 times that of bulk salt powder by the 12th cycle, whereas the bulk salt degraded by 78.5%. In situ environmental scanning electron microscope observations during hydration/dehydration cycles demonstrated that swelling and deliquescence induced redistribution of salt hydrates within the metal foam while preserving essential open pores for heat and mass transfer, along with the specific reaction surface, which explains the amelioration of the composite thermochemical performance
Méthode numérique garantie à complexité polynomiale, pour étudier la stabilité des systèmes non linéaires à n-dimensions indépendants du temps avec perturbations bornées
No full textInternational audienceThe stability analysis of nonlinear continuous systems often requires manual calculation, which can become time-consuming when dealing with complex systems. Some works use positive invariant sets to discuss stability. These sets can be numerically approximated using Interval analysis but the computational complexity is exponential. In this paper, we propose a computational tractable numerical but guaranteed method based on Interval analysis to verify the robust positive invariance of ellipsoids to automatize the study of n-dimensional nonlinear systems' stability. This method relies on a fast enclosure of a state integration by an Euler method. Interval analysis guarantees the results of the developed algorithms. Several examples show the effectiveness of the proposed approaches on -dimensional non-asymptotical continuous systems subject to bounded perturbation
Navigation among movable obstacles using machine learning based total time cost optimization
No full textInternational audienceMost navigation approaches treat obstacles as static objects and choose to bypass them. However, the detour could be costly or could lead to failures in indoor environments. The recently developed navigation among movable obstacles (NAMO) methods prefer to remove all the movable obstacles blocking the way, which might be not the best choice when planning and moving obstacles takes a long time. We propose a pipeline where the robot solves the NAMO problems by optimizing the total time to reach the goal. This is achieved by a supervised learning approach that can predict the time of planning and performing obstacle motion before actually doing it if this leads to faster goal reaching. Besides, a pose generator based on reinforcement learning is proposed to decide where the robot can move the obstacle. The method is evaluated in two kinds of simulation environments and the results demonstrate its advantages compared to the classical bypass and obstacle removal strategies
Systematic review of technologies to collaborate and co-educate students with special educational needs and supporting their schooling
No full textInternational audienceSince 1994, the inclusion of students with special educational needs (SEN) has been a vital part of the educational system (UNESCO, 1994). In the early 2000s, educational systems underwent reforms to accommodate this change, leading to increased communication and collaboration efforts between families and educational partners (Wehmeyer & Patton, 2017). These efforts are supported by the growth of digital technologies (Kefallinou et al., 2020; Zallio & Ohashi, 2022). Various models of family-professional collaboration, such as the "Sunshine Model" (Haines et al., 2017), "Whole School Model" (Lewallen et al., 2015), "Smart Holistic Model" (Hafidh et al., 2019), and polycentric approaches (Ebersold & Detraux, 2013), have been developed to involve the broader educational community.Despite the integration of technologies and the recognized importance of collaboration, limited research has been conducted on the potential of collaborative technologies in the educational context for SEN. However, relevant stakeholders endorse their use.To address this gap, a systematic review of international literature was conducted to identify collaborative technologies for the inclusion of SEN, along with their advantages and limitations. Out of 1360 identified articles, 10 were selected for analysis.These 10 articles focused on 8 different digital technologies that facilitate collaboration between families, education, and healthcare actors. The technologies were developed using various methodologies and aimed at different communication and collaboration objectives. Some technologies focused on communication related to student behavior or school activities, while others emphasized collaboration related to the student's inclusion project.We will present each of these technologies, their development context, as well as their advantages and limitations. We will hightlight their relevance to the different theoretical models applied to family-professional collaboration, and their contributions Finally, we will highlight the contributions of collaborative technologies to promoting SEN inclusion and reducing educational inequalities
The effect of interphase and agglomeration on the mechanical properties of aluminum matrix nanocomposites reinforced with carbon nanotubes
No full textInternational audienceThe interphase phenomena are a critical problem for estimating the mechanical behavior of carbon nanotube-reinforced aluminum composites. In this research, the Aluminum-carbide (Al4C3) interphase and carbon nanotubes (CNTs) agglomeration effects on the mechanical properties of Aluminum /Carbon nanotubes composites are investigated using a numerical micromechanical model. Moreover, the impacts of the CNTs fraction, agglomeration, Al4C3 interphase, and their diameter on the elastic modulus of Aluminum (Al) composites are explored. The results demonstrated the effect of CNTs agglomeration and Al4C3 interphase on Young's modulus of Al composites significantly when the CNT fraction increases; In addition, it observed that with increasing interphase thickness, Young's modulus of Al composites increases and is changed with variation of agglomeration shape. The Literature's experimental results validated the applicability of the present finite element (FE) model. The results of this study are hard evidence for CNT/ Aluminum composites creating potential applications in industry, especially for automobile and aircraft fields
Nonequilibrium warm dense matter investigated with laser–plasma-based XANES down to the femtosecond
No full textInternational audienceThe use of laser–plasma-based x-ray sources is discussed, with a view to carrying out time-resolved x-ray absorption spectroscopy measurements, down to the femtosecond timescale. A review of recent experiments performed by our team is presented. They concern the study of the nonequilibrium transition of metals from solid to the warm dense regime, which imposes specific constraints (the sample being destroyed after each shot). Particular attention is paid to the description of experimental devices and methodologies. Two main types of x-ray sources are compared, respectively, based on the emission of a hot plasma, and on the betatron radiation from relativistic electrons accelerated by laser
Chip-Interleaved DSSS for Energy-Efficient Physical Layer Encryption
No full textInternational audienceTraditional methods for ensuring secure communications typically rely on encryption, which necessitates some form of coordination between the transmitter and the receiver. The Direct Sequence Spread Spectrum modulation can introduce some security at the physical layer but this technique must be combined with other technologies. Physical layer encryption techniques offer an alternative approach by taking advantage of transmit arrays to introduce beamformed noise. These techniques guarantee a certain level of confidentiality without requiring neither a heavy coordination nor losing time for secret key establishment, which make these techniques very attractive in particular for military and secured communications. However, the proposed solutions in the literature suffer from several limitations, and in particular, poor energy efficiency. To address this issue, we propose an original solution for physical layer encryption that does not spoil any energy with a signal mask by taking advantage of the wiretap channel inherent degradation introduced by the spatial chip interleaving over the transmitter antennas. Our simulations confirm that our proposal guarantees a considerable level of confidentiality without any energy loss
Palladium‐Catalyzed Regioselective peri ‐ and ortho ‐Halogenation of 1‐Naphthaldehydes: Application to the Synthesis of Polycyclic Natural Product Skeletons
No full textInternational audienceHerein, a regioselective bromination or chlorination reaction of 1‐naphthaldehydes is described. Without additive, the palladium‐catalyzed C−H halogenation showed a C8‐regioselectivity, whereas the formation of an aromatic imine intermediate allowed a switch to a C2‐reactivity. Mechanistic studies and DFT calculations were performed to explain the regioselectivity and the synthesized halogenated products were used as key building blocks to access polycyclic natural product skeletons